1. Field of the Invention
The present invention relates to an imaging device array, an optical writing unit including the imaging device array, and an image forming apparatus including the optical writing unit.
2. Description of the Background Art
In parallel with the size reduction of a digital copier, printer, digital facsimile apparatus or similar image forming apparatus, there is an increasing demand for the size reduction of an optical writing unit that writes an image on a photoconductive element. Small size, optical writing units include one using a solid-state writing system in which an imaging device array focuses light beams issuing from a light emitting device array on a photoconductive element in the form of beam spots. The light emitting device array is implemented as an LED (Light Emitting Diode) array or an organic EL (ElectroLuminescence) device array. The solid-state writing system makes an optical path between the light source and the photoconductive element extremely short to thereby make the optical writing unit and therefore an image forming apparatus compact. Basically, the imaging device array has a number of imaging devices arranged in an array in one-to-one correspondence to the light emitting elements of the light emitting device array. A rod lens array is one of conventional imaging device arrays.
The problem with the imaging device array of the type described is that needless light, i.e., ghost light and flare light are condensed on an image plane at positions other than expected positions. Ghost light is condensed at an unexpected position to a certain degree, forming a beam spot. Flare light is substantially homogeneously distributed on the image plane without being condensed. When an image forming apparatus using the conventional imaging device array forms an image, such ghost light and flare light degrade the quality of the image.
It is an object of the present invention to provide an imaging device array capable of effectively reducing the influence of ghost light and flare light.
It is another object of the present invention to provide an optical writing unit using the above imaging device array and an image forming apparatus including the optical writing unit.
In accordance with the present invention, an imaging device array includes a plurality of unit imaging devices each including a lens portion made up of a first lens surface to which a light beam for imaging is incident and a second lens surface from which the light beam is output, and a roof prism portion for reflecting the light beam incident via the first lens surface toward the second lens surface. The unit imaging devices are arranged integrally with each other such that the first lens surfaces, second lens surfaces and roof prism portions each are arranged in a respective array. Light attenuating members each intervene between nearby lens portions for attenuating light propagating between the lens portions. The light attenuating members have an attenuation ratio xcex1 smaller than 0.25 each.
An optical writing unit using the above imaging device array and an image forming apparatus including the optical writing unit are also disclosed.